1. Field of the Invention
The present invention relates to a magnetic tape cassette. Particularly, it relates to a magnetic tape cassette provided with a locking means for locking reels.
2. Description of Prior Art
There has so far been provided in a magnetic tape cassette, especially, in a video tape cassette a locking means for locking rotation of reels held in the tape cassette during non-use, for the purpose of preventing rewinding of the magnetic tape during preservation during non-use and transportation of the tape cassette.
FIG. 1 shows a conventional locking means. The construction of a magnetic tape cassette with the conventional locking means will be described with reference to FIG. 2, which shows an embodiment of the present invention, by assuming that the locking means according to the present invention is replaced by the conventional locking means as shown in FIG. 1. A pair of reels 5, 7 for a magnetic tape 3 are put in a magnetic tape cassette body which is constituted by an upper half casing (not shown) and a lower half casing. The shaft of each of the reels 5, 7 is loosely fitted to a pair of through holes 9, 11 formed in the lower half casing 1 respectively. Each of the shafts is adapted to be driven by each driving shaft extending upwardly from a magnetic tape recorder. The outer peripheral edges of the lower flanges 13, 15 of the reels 5, 7 are respectively provided with saw-teeth like notches 14, 16. In the central part of the back wall 17 of the lower half casing 1, there are formed a pair of guide pieces 19, 21 between which a guiding channel 23 is formed extending between the front and back of the magnetic tape cassette. In the guiding channel 23, a locking means 27 is fitted with its rear part being pushed forwardly by a spring 25 as shown in FIG. 1 so that when the magnetic tape cassette is mounted on the tape recorder, the locking means 27 is slidingly moved backward. A pair of flexible pawls 29, 31 having elasticity are fitted to or formed integrally with the front part of the locking means 27. The flexible pawls are adapted to be normally opened in the directions shown by arrow marks. The opening of the flexible pawls 29, 31 is restricted by means of a pair of pins 33, 35 provided in the front of the guiding channel 23 of the lower half casing 1. When the magnetic tape cassette is not mounted on the tape recorder, the spring 25 pushes the locking means 27 forwardly (namely, in the direction of arrow mark 37 in FIG. 1) to make the flexible pawls 29, 31 opened whereby the flexible pawls are engaged with the saw-teeth like notches 14, 16 of the lower flanges 13, 15 of the reels 5, 7. When the magnetic tape cassette is mounted on the tape recorder, the locking means is pushed backwardly (namely, in the direction opposite to the arrow mark 37 in FIG. 1) by an operating means extending from a through hole formed in the bottom surface of the locking means 27 in the lower half casing 1. Backward movement of the locking means releases engagement of the flexible pawls with the reels 5, 7 and the pins 33, 35 close the flexible pawls inwardly.
Magnetic tape cassettes are often left for a long time while they are mounted on tape recorders, on account of which there causes thermal deformation in the flexible pawls 29, 31 of the locking means in the closing state under application of stress. Accordingly, when the locking means is returned to the locking position, engagement of the flexible pawls with the reels may not be attained. In such case, a wound magnetic tape becomes loose and fitting operation of the magnetic tape to a tape running system of a tape recorder can not be performed smoothly.